The Internet maintains two principal namespaces, the domain name hierarchy and the Internet Protocol (IP) address space. The DNS maintains the domain name hierarchy and provides translation services between the domain name hierarchy and the IP address space.
A host is any computer, service, or resource connected to the Internet or a private data network. A domain name is a textual string, which uses words or phrases from a language such that a human can memorize the string as a name of the host. The DNS not only translates a human-memorizable domain name to a computer-usable numerical IP address, but also associates various other information with the domain name as a DNS record of the corresponding host.
The DNS distributes the responsibility of assigning domain names and mapping those names to IP addresses by designating Authoritative Domain Name Servers (ADNS) for each domain. An ADNS is responsible for the definite and authoritative information—the DNS records—for those domain names that are configured on that ADNS by an administrator.
The Domain Name System also defines the DNS protocol, a detailed specification of the data structures and data communication exchanges used in DNS, as part of the Internet Protocol Suite. A DNS server is a server system or application that stores the DNS records for a set of domain names. A DNS server can be local to a data network, such as a local area network of a corporation or another entity.
A client application can request to resolve a domain name to an IP address by sending a name resolution request to a local DNS server (LDNS). If the LDNS has an entry for the requested domain name in the LDNS' database, the LDNS responds with an answer to the request from that database. If the LDNS does not have an entry for the requested domain name in the LDNS' database, the LDNS queries the ADNS for that domain and communicates the answer received from the ADNS.
Regardless of where the information to resolve the requested name to the IP address comes from, a DNS server always responds to a name resolution request truthfully based on the contents of that information. In other words, regardless of where the resolved domain name might direct the client application, the DNS server always provides the exact IP address that corresponds to the domain name in local or obtained information.